1. Field of the Invention
The present invention relates to a sensor to measure the position and velocity of movement of a piston in a cylinder. More particularly, the present invention relates to a magnetostrictive linear displacement transducer for use in a vehicle suspension strut.
2. Background Art
Various devices have been advanced to measure the distance traveled by a piston in a cylinder. One common application is determining the movement of the piston in a hydraulic, pneumatic, or hydro-pneumatic vehicle strut suspension, where the piston moves axially in a cylinder filled with at least one damping medium. See U.S. Pat. Nos. 4,502,006; 4,638,670; and 5,233,293, each of which discloses a displacement sensor to perform this function. None of the devices so far advanced has been widely accepted in the automotive industry. Although many systems can accurately measure motion of a piston in a cylinder or linear displacement or angular displacement, a simple transducer that can be easily incorporated into, for example, the strut suspension system to keep manufacturing costs down is still desired by many.
A vehicle suspension strut is disclosed which includes a housing having a chamber and a piston slidably disposed in the chamber. A piston rod is connected to the piston and extends out of the housing. The piston rod includes a bore extending longitudinally therein. A magnetostrictive transducer provides an output signal indicative of the position and/or velocity of the piston with respect to the housing. The magnetostrictive transducer includes a magnetostrictive waveguide disposed in the bore and a magnet joined to the housing that is operably coupled to the magnetostrictive waveguide.
Another aspect of the present invention is a magnetostrictive transducer having a waveguide secured by a suspension sleeve fully surrounding the waveguide for use as automotive devices for applications requiring linear and/or angular measurement such as brake peddle position, steering wheel position, throttle position, mirror position and air valve position. The suspension sleeve and the waveguide are disposed in an inner cavity of an enclosure tube. In the preferred embodiment, the present invention further includes pins or connectors to electrically connect the waveguide assembly to an electric circuit that generates electric pulses and provides an output signal corresponding to, for example, the time required for torsional strain wave pulses to be received by a coil. A damping element is secured to the waveguide with heat shrinkable tubing or some other means, and dampens strain pulses not used by the electrical circuit. The suspension sleeve also serves to mechanically isolate the waveguide assembly from shock, vibration and contact with the enclosure tube.